Recoiless
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Basic Information

It's a basic law of physics1 that every action creates an equal and opposite reaction and thus to launch a round of ammunition from a missile weapon, you need to dispose of as much energy as it takes to launch the round acting in the opposite direction. We call this recoil.

For primitive (i.e. pre-gunpowder) weapons, this isn't much of a problem since in general the amount of energy imparted is low and the action of firing tends to favour the firer. Not so with the advent of gunpowder - firearms impart a lot of energy to their shot in a short burst, and generate an equivalent hard, sudden kick of recoil. There are various ways of dealing with this;

  1. You can put up with it - this was a common solution until the mid to late nineteenth century. This lead to weapons that were inaccurate and uncomfortable, painful and/or dangerous to fire - artillery in particular tended to leap about everywhere, killing slow moving or careless operators and needing to be relaid after each shot. This technique is used to this day in a lot of single action weapons and in smaller pieces where the recoil is pretty low anyway. It's also more or less unavoidable in revolvers.
  2. You can make the weapon (a lot) heavier to adsorb the energy - the slightly less ugly cousin of option #1. A larger, heavier weapon will move less under the influence of the same energy. This design feature shouldn't be overlooked, even in small arms, where mass is unpopular, but reducing it can make a weapon surprisingly uncontrollable. This is a more popular technique in heavy weapons and ordnance though - where the piece doesn't need to be carried, then it can be stabilised by its own mass and the energy dumped into the ground. Mortars often don't go far beyond this in design sophistication.
  3. You can soak the energy up mechanically - often by using the recoil to drive a semi or fully automatic action. This can work surprisingly well, but where the recoil is high, a mechanism poweful enough to adsorb it can be fairly heavy in its own right. Heavy and mechanically complicated.
  4. You can cheat.

Cheating, in this context, meaning using recoiless weapons. Actually "recoiless" is a bit of a con - they still generate recoil, but the amount of it that gets transmitted to the mounting or the operator is proportionally tiny. The trick is ensuring that the launch of the projectile doesn't get to push on the launcher and this is almost always done by using some kind of rocket or otherwise ejecting countermass. Either the round disperses all of its energy backwards at time of firing as a backblast, or (as in a gyrojet and many missiles) the round does most of its accelerating after launch.

The first recoiless weapon to see general issue was the German Leichtgeschutz 40 - a light weapon developed for airborne use that actually fired regular 75mm artillery shells, using a complicated venturi firing system to generate a back blast that counteracted the recoil. The weapons were deployed in the 1940 landings on Crete and examples were captured by the allies, whilst the Germans were so pleased with it that they developed a 105mm version. And then they abandoned airborne operations and put very little further effort into recoiless artillery.

The US, by contrast, took quite an interest in the examples they received from British intelligence and, once German technology had miscegenated with their indigenous programme a variety of weapons were born. Most barely made it to WW2 but one that did was the Launcher, M1. Better known as the bazooka. A straight through, rocket firing weapon that was easily man-portable and delivered a shaped charge round that was extremely effective against enemy armour. Several British weapons were also developed, but they too failed to make it to the war.

Unsurprisingly the Germans liked the look of what had become of their technology and reclaimed it, developing the Panzershcreck and the even more innovative Panzerfaust (which was arguably the first LAW).

The lightweight recoiless weapon, firing a shaped charge rocket has become the more-or-less unquestioned basis of every anti-tank-weapon currently in service - and seems unlikely to be replaced any time soon.

Despite the benefits of the technology, there are still significant drawbacks - the main one being the backblast generated by most recoiless weapons, which is normally dangerous to anyone standing behind the weapon and can even harm the operator if the weapon is fired in a confined space or too close to an obstacle. Backblast will also give the firer's position away and may ignite flammable terrain. Some modern designs eject water or plastic as countermass, which is less conspicous and dangerous, but is still not fun to be caught in.

Probably the most outlandish use of recoiless technology would be the M-388 "Davy Crockett" launcher for a tactical nuclear weapon.

Sources

Bibliography
1. full source reference

Game and Story Use

  • Note that in a lot of cases - particularly those of heavy anti tank weapons which take a long time to arm - the backblast may be a more effective weapon against enemy infantry that the round. Watch the PC or action hero flip his launcher around and roast his attackers with the backblast. Bit cinematic but very rule of cool.
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